Rollers carrying surface designs for use in printing, embossing and the like



United States Patent 3,283,714 ROLLERS CARRYING SURFACE DESIGNS FOR USE IN PRINTING, EMBOSSING AND THE LIKE Albert S. Carpenter, Sutton Coldfield, and Walter W. G.

Norris, Downend, Bristol, England, assignors to Couraulds Limited, London, England, a British company No Drawing. Filed May 21, 1963, Ser. No. 282,122 Claims priority, application Great Britain, May 23, 1962, 19,799/ 62; Sept. 5, 1%2, 33,979/62 7 Claims. (Cl. 101-4011) This invention relates to a plate, roller or the like device carrying a raised or indented design for use in printing, embossing or the like for the purpose of reproducing reading matter, photographs, patterns, drawings, advertisements or the like (all of which, together with their inverse images which appear on the printing or embossing surface, are hereinafter for brevity included in the general term design) which are to be reproduced repeatedly by known methods on paper, cardboard, fabrics, films (for example, transparent packaging films) or the like. For the sake of brevity in the ensuing description such plates, rollers and the like devices will be referred to as formes.

In accordance with the present invention a process for the production of a forme for use in a relief or intaglio printing process includes the step of casting a liquid material, preferably a liquid polymerisable material, inside a hollow axially rotatable circular cylinder bearing the required design on its internal surface, by the process commonly referred to as centrifugal casting wherein solidification of the material takes place during high speed rotation of the hollow cylinder to form a circular cylindrical cast shell.

The cast shell produced in the process according to the invention may be mounted on a shaft to provide a forme for use as a printing or embossing roller. Alternatively, sections may be cut from the cast shell and mounted on rollers for use, by conventional procedures, in relief or intaglio printing processes. Cast shells which have been made of flexible or heat-softenable material may be made to conform to a different curvature or may be flattened to provide formes for use as printing or embossing plates.

In known, widely used etching processes for making raised or indented surfaces for relief or intaglio printing by photo-mechanical processes, use is made of the insolubilising effect of light on sensitized compositions of gelatine and other colloids, hereinafter referred to as light-sensitive colloids. Films of such compositions supported on paper backings, and generally known as carbon tissue or pigment paper, are photosensitized by treatment with, for example, amonium bichromate, exposed to a photographic image, transferred to a corrosible surface for example of copper and then washed with Water to remove the unexposed portions and so provide a resist finish in the desired design through which etching of the corrosible substrate by a corrosive fluid may take place.

In accordance with one embodiment of the present invention, similar light-sensitive colloid films are used for forming the required design indented for relief printing or raised for intaglio printing, on the internal surface of the axially rotating cylinder.

One procedure which may be employed is to form the relief or indented design on the inside of the cylinder by transferring the light-sensitive colloid composition from sensitized and photographic-ally exposed carbon tissue to a flexible but laterally inextensible material, developing with warm water to remove those parts which have received no light (these operations being carried out 3,283,714 Patented Nov. 8, 1966 in known manner) and then curving the flexible material with the colloid-coated surface innermost, and fitting it inside the rotatable cylinder. It may be closely fixed to the internal surface of the cylinder with an adhesive or alternatively, rapid rotation of the cylind r may be caused to press it tightly against the internal surface of the cylinder by centrifugal force to become, in effect with its colloid-coated surface, an integral part of the rotating cylinder.

As an alternative to this procedure, the light-sensitive colloid composition of the photographically exposed carbon tissue may be transferred directly to the inside of the axially rotatable cylinder before washing with warm water to develop the raised or indented design. To facilitate transference of the colloid composition and the subsequent removal of the cast shell, the cylinder may be constructed in two or more longitudinal. sections which can be readily dismantled.

In accordance with another embodiment of the invention, which avoids transferring the colloid composition from a paper backing, a light-sensitive colloid composition may be coated on to a flexible but laterally inextensible backing material, the normally included separation layer of carbon tissue being omitted. This coating is then sensitized, photographically exposed, washed to develop the raised or indented design, curved and inserted directly into the rotatable cylinder as described above.

In accordance with a further embodiment of the invention, a light-sensitive colloid composition may itself be centrifugally deposited as a thin film on the internal surface of the rotating cylinder by introducing it as an aqueous solution into the rapidly rotating cylinder and evaporating off the water during rotation. The steps of sensitization, exposure and washing then take place with the colloid composition already in position on the cylinder wall. The cylinder used may also be constructed in sections as described above to facilitate exposure and subsequent removal 'of the cast shell.

Other methods of forming a raised or indented surface in the desired design on the roller may be used. For example, in the technique known as xerography, use is made of the photoelectric properties of certain materials to deposit, for example, finely powdered, fusible resin selectively in the design of a photographic image. The resin may be fused to form a coherent raised design adhering to the surface of the thin flexible plate on which it was deposited and this plate may be curved and fitted inside the rotatable cylinder, as described above, to form the design-bearing surface of the cylinder assembly.

The liquid material used for the casting may be any type or resin or mouldable material which is initially in a liquid form but which can subsequently be caused to become solid, for example, by a polymerization reaction, during the centrifugal casting operation. It will be appreciated that the term polymerization refers to both condensation polymerization and addition polymerization. The material may for example be a liquid resin such as a liquid epoxy or polyester resin which may be mixed with a catalyst so that setting of the resin takes place without external heating; alternatively the material may be one which polymerizes on the application of heat and, in this case, the rotatable cylinder will be suitably heated to cause the required polymerization of the material. An example of such a material is caprolactam containing an alkali catalyst such as sodium metal and an acyl compound activator such as N-acetyl caprolactarn, such a mixture being cast at temperatures of the order of -180 C. Another example is styrene either in the monomeric form or partially polymerized, to which a polymerization initiator has been added. Liquid silicone resins which give rubbery products may also be used, a catalyst being added to cause setting of the resin during the casting.

In addition to liquid polymerizable materials, other materials which may be readily converted from the liquid to the sol-id or rubbery form may be used to form the circular cylindrical shell in the centrifugal casting step. For example, a low melting metal alloy may be liquified by heat, introduced into the heated rotatable cylinder assembly and allowed to solidify on cooling while the cylinder is in high speed rotation. Alternatively, an aqueous dispersion of a polymeric product which gives a coherent mass on removal of the water may be introduced into the cylinder and the water removed by evaporation by means of heating and/or an air current passed into the cylinder While it is in high speed rotation.

For the casting of the cylindrical shell, the cylinder is fitted with endplates which prevent the outflow of liquid from its interior, one end plate being axially perforated to allow the introduction of the liquid material from which the cast shell is to be formed. The precise details of the casting process will depend upon the character of the casting material. It is essential however, in all cases,

that the cylinder should be in continuous uniform high speed axial rotation during the time that the material is being converted from the liquid to the solid state.

In roller printing, and particularly in gravure work it is important that the roller should be as close as possible to an exactly circular cylindrical shape. Also, if two or more colours are being printed, it is essential that all rollers should be of correct circumference so as to give accurate register of the different colours.

Some polymerizable materials otherwise suitable for use in carrying out the invention have a tendency to shrink either as a result of polymerization or (when polyrnerization takes place at elevated temperatures) from cooling after polymerization. Some materials, for example polyester and epoxy resins have high polymerization exotherms and distortion and contraction may occur when polymerization is allowed to take place in large bulks from which diffusion of heat of polymerization is slow.

However, as such polymerizable materials are manufactured in a variety of grades and different catalysts and different polymerization conditions may be used, the materials and conditions should be chosen to minimize shrinkage. Additional methods of reducing shrinkage can also be used such as by incorporating fillers and reinforcing agents into the polymerizable composition.

It is advantageous, from this aspect, when using epoxy and polyester resins for the formation of the shell, to cast the latter in a number of concentric layers by the succes sive addition at intervals of several small resin charges while the casting cylinder is in continuous rotation, each charge being allowed to gel before the addition of the next. In this way, shrinkage and distortion can be virtually eliminated and any desired shell thickness may be 'built up.

An advantage of using a flexible sheet with the raised design on its surface as a liner for the axially rotating cylinder is that under the desirable conditions of zero shrinkage, the cast shell and liner can be slid out of the casting cylinder as one entity without damaging the patterned face of the shell. The sheet may then be peeled Off the shell.

Resin castings may be strengthened if desired, for example, by removing one end plate of the rotating cylinder assembly after at least one resin layer has been allowed to solidify and take the required design, introducing glass fibre (in the form commonly referred to as chopped strand mat) so that it conforms roughly to the shape of the internal surface of the cast cylinder, reassembling and casting more resin in and on the glass fibre while the cylinder is once more in rotation.

For a further method of strengthening, a second hollow rigid cylinder of external diameter somewhat less than the internal diameter of the casting cylinder may be positioned co-axially inside the casting cylinder, and in such a way that it will rotate with it. During centrifugal casting, the casting material fills the annular space between the cylinders. With this method the second rigid cylinder becomes embedded in the material as an integral part of the casting produced, and since its outer surface is covered only by a relatively thin layer of the solid material it reduces any changes in the diameter or distortion due to shrinkage to a minimum. The second rigid cylinder may conveniently be formed from metal tube, or from pre-formed, fibre-reinforced resin tube. In order to facilitate the flow of the material into the annular space, the second rigid cylinder may be somewhat shorter than the outer cylinder or may have perforations, particularly at its ends. It may have surface indentations or markings, or may be perforated throughout its length to facilitate keying of the material to it.

The second rigid cylinder may be mounted in the outer rigid cylinder by some means which may be dismantled readily so that after solidification the composite shell with the second rigid cylinder embedded in it may be removed from the outer cylinder. For example, it may be located by projections on the end plates which blank off the ends of the outer cylinder.

In printing with rollers on to material in continuous roll form, it is necessary to produce rollers of precise circumferential dimensions, to ensure an accurate repeat distance on the printed sheet.

One convenient method of accomplishing this is as follows. A liquid castable material such as a liquid polymerizable material or a plaster of Paris/ water mixture or a low-melting metal composition made liquid by heat is introduced in predetermined quantity into the interior of an axially rotatable rigid cylinder having suitably blanked off ends to prevent the liquid castable material from running out and is centrifugally cast therein to form a composite cylindrical tube. The quantity of castable material is such that the internal circumference of the composite cylindrical tube is that required to give the required circumferential measurement to the shell of a printing roller subsequently cast into it by any of the means described above, but at a temperature at which the precast material is stable.

In an alternative method, a rigid, axially rotatable cylinder of length greater than that required for the final printing roller may be divided internally by a wier device into a main compartment of the desired roller length and an overflow compartment. An excess of the liquid castable material is placed in the main compartment and, in the preparatory centrifugal casting operation, the excess over that required to give the composite cylinder of the required internal circumference, overflows into the overflow compartment. The overflow compartment is blanked off and the composite cylinder used as described above.

In continuous multi-stage printing on certain materials, such as regenerated cellulose film, it is common experience that longitudinal distortion of the film may take place during its passage between the various stages. Rollers of accurately graded sizes are required to accommodate these distortions and give accurate register of the successive impressions. Such rollers may readily be fabricated by either of the methods just described.

A further advantage of these methods of preparing the outer cylinder for the main casting process is that no accurate machining of the outer cylinder is required. The centrifugal casting of the surface on which the shell is subsequently cast in a similar operation ensures that it is of precise circular cylindrical shape.

A feature of the centrifugal method of casting is that air bubbles which might be entrapped in the casting liquid are driven inwards by the rotation and do not cause imperfections on the final printing or embossing surface of the forme. On the other hand, reinforcing and hardening filler powders which may be incorporated, being more dense, in general, than the casting material tend to be thrown to the outer surface where their increased concentration has advantageous and economical effects.

When light-sensitive colloid compositions are used to form the moulding surface, they may be first conditioned to particular humidity conditions. These colloids can absorb moisture under high humidity conditions and thereby swell. In the production of a gravure printing roller, for example, it may be necessary to ensure undistorted cavity shape and size by conditioning the colloid to a particular humidity immediately before the casting operation. The swelling of these colloids at high humidity or an immersion in water may be advantageously employed to give increased cavity size in gravure printing. Conditioning at a fairly high humidity has been found advantageous in some cases, particularly when using polyester resins, in avoiding adhesion between the colloid composition and the cast resin. Separation has been clean and it has been possible to cast several shells from the same mould without loss of precision.

The invention is illustrated by the following examples in which parts and percentages are by weight.

Example 1 The design sheet was prepared according to known techniques as follows:

Carbon tissue having an effective gelatine composition depth of 0.0025 inch was photo-sensitized by immersion in aqueous bichro-mate solution, squeegeed on to a polished stainless steel plate, dried and removed from the steel sheet. It was then mounted in a printing frame behind a photographic negative and gravure screen having 150 lines mr inch and a ratio of 2:1 and exposed to light from a carbon are for 12 minutes. This time had been found to be suitable from a previous series of test exposures. The gelatine face of the exposed tissue was squeegeed on to a polished brass sheet of 0.008 inch thickness, dried, and then immersed in warm water. When the water had penetrated to the separation layer and softened it, the paper backing was peeled off and the warm water gently worked over the exposed gelatine surface to dissolve away those parts which had not been insolubilised by the light. When the raised image had been developed the sheet was washed in clear water and dried in warm air.

The centrifugal casting equipment used consisted of a horizontal hollow copper cylinder heavily chromium plated on its circular cylindrical internal surface, and fitted with readily removable end plates. One end plate was connected to a variable speed motor via a flexible coupling and the other had a hollow extension serving as a charging port.

The internal surface of the cylinder and the inwardly directed surfaces of the end plates were lightly covered with a silicone grease and the brass sheet, after being cut to size and rolled into a roughly cylindrical shape corresponding approximately to the shape of the internal surface of the cylinder, was very lightly greased on its outer face, compressed to a slightly more curved shape and inserted in the cylinder. It sprang loosely into place and light pressure using a lint-free cloth caused it to adhere closely by virtue of the grease on the contacting faces. Extra pressure was used along the join to expel any excess grease.

The casting apparatus was assembled and rotated at 1000 rpm. for five minutes to force the brass sheet into firm close contact with the internal surface of the cylinder.

Two hundred parts of a commercial epoxy resin (Shell, Epikote 828) were mixed with 50 parts of an amine curing catalyst (Shell, Epikure RTU) and the mixture introduced into the rotating cylinder assembly by means of the charging port sufficient to form a deposit about 0.08

inch thick. After six hours the rotational speed was reduced to 500 rpm. and a further charge of resin added. Two other similar charges were added at subsequent six-hourly intervals.

When the last resin charge had been allowed to set, rotation was stopped, the apparatus dismantled and the cast shell removed. The cast was stood. in warm water containing a detergent for five minutes and the adhering gelatine removed by light brushing. It was then wiped dry and left (on end) in an oven at C. for 12 hours to complete the hardening.

The thin raised longitudinal line of resin corresponding with the gap between the ends of the brass sheet was then removed to give a continuous curve without imperfections by scraping with a sharp edge, gently rubbing with blunted fine emery paper and finally polishing.

The final shell casting was mounted on a shaft with suitable end attachments to give a gravure printing roller. Prints were obtained from it in continuous operations on regenerated cellulose film, on polyethylene film and on paper by the customary procedures. The prints compared favourably with those from conventional chromium plated copper gravure rollers.

In a variation of the above procedure, the first resin charge may also contain 50 percent (based on the resin) of 300 mesh slate powder.

Example 2 In a similar series of steps to those described in Example l, the first charge consisted of Parts Liquid polyester resin (Bakelite DSR/l9ll48) 200 Peroxide catalyst 4 Cobalt activator 4 The inside of a centrifugal casting cylinder similar to that described in Example 1 was sand blasted and cleaned.

After assembling the equipment, an epoxy resin charge of Parts Epikote 828 200 Epikure RTU 50 was centrifugally cast inside. The resin coated cylinder was then used as a casting cylinder in a similar series of operations as described in Example 1, to produce a shell casting.

Example 4 A screened negative was produced by known method using a magenta screen and this was then used in a series of steps similar to those described in Example 1 for making first a relief image of gelatine composition on brass sheet and then, from this, a cast shell which was mounted on a shaft to provide an invert half-tone gravure roller.

What we claim is:

1. A process for the production of a cylindrical forme for use in relief or intaglio printing which comprises forming a hollow axially rotatable cylinder having a raised or indented design on its internal surface, casting a first charge of a liquid material capable of polymerization within said cylinder while rotating said cylinder, polymerizing said first charge in situ in contact with said design while rotating said cylinder, and subsequently casting additional liquid polymerizable material and polymerizing said additional material while rotating said cylinder.

2. A process as claimed in claim 1 wherein the material capable of being polymerized is an epoxy resin.

3. A process as claimed in claim 1 wherein the material capable of being polymerized is a polyester resin.

4. The process claimed in claim 1 wherein said additional material is furnished as a plurality of charges, each charge being polymerized before the next charge is cast.

5. The process claimed in claim 4 wherein at least one of said additional charges contains reinforcing fibres.

6. The method claimed in claim 1 and comprising forming the hollow axially rotatable cylinder having a raised or indented design on its internal surface by trans-' ferring a light sensitive colloid composition from a sensitized and photographically exposed carbon tissue to a flexible sheet, developing the colloid composition to form an image, curving the sheet with the colloid innermost and fitting it inside a hollow, rotatable cylinder.

7. A process for the production of a cylindrical forme for use in relief or intaglio printing which comprises forming a first hollow axially rotatable cylinder having a raised or indented design on its internal surface, positioning a second hollow rotatable cylinder having a lesser diameter than said first cylinder coaxially within said first cylinder to form an annular space between said cylinders, casting a first charge of a liquid material capable of polymerization Within said annular space While rotating said cylinders, polymerizing said first charge in situ in contact with said design while rotating said cylinders and subsequently casting additional liquid polymerizable material in said annular space and polymerizing said additional material while rotating said cylinders.

References Cited by the Examiner DAVID KLEIN, Primary Examiner.

H. STRNISHA, Assistant Examiner. 

1. A PROCESS FOR THE PRODUCTION OF A CYLINDRICAL FORME FOR USE IN RELIEF OR INTAGLIO PRINTING WHICH COMPRISES FORMING A HOLLOW AXIALLY ROTATABLE CYLINDER HAVING A RAISED OR INDENTED DESIGN ON ITS INTERNAL SURFACE, CASTING A FIRST CHARGE OF A LIQUID MATERIAL CAPABLE OF POLYMERIZATION WITHIN SAID CYLINDER WHILE ROTATING SAID CYLINDER, POLYMERIZING SAID FIRST CHARGE IN SITU IN CONTACT WITH SAID DESIGN WHILE ROTATING SAID CYLINDER, AND SUBSEQUENTLY CASTING ADDITIONAL LIQUID POLYMERIZABLE MATERIAL AND POLYMERIZING SAID ADDITIONAL MATERIAL WHILE ROTATING SAID CYLINDER.
 7. A PROCESS FOR THE PRODUCTION OF A CYLINDRICAL FORME FOR USE IN RELIEF OR INTAGLIO PRINTING WHICH COMPRISES FORMING A FIRST HOLLOW AXIALLY ROTATABLE CYLINDER HAVING A RAISED OR INDENTED DESIGN ON ITS INTERNAL SURFACE, POSITIONING A SECOND HOLLOW ROTATABLE CYLINDER HAVING A LESSER DIAMETER THAN SAID FIRST CYLINDER COAXIALLY WITHIN SAID FIRST CYLINDER TO FORM AN ANNULAR SPACE BETWEEN SAID CYLINDERS, CASTING A FIRST CHARGE OF A LIQUID MATERIAL CAPABLE OF POLYMERIZATION WITHIN SAID ANNULAR SPACE WHILE ROTATING SAID CYLINDERS, POLYMERIZING SAID FIRST CHARGE IN SITU IN CONTACT WITH SAID DESIGN WHILE ROTATING SAID CYLINDERS AND SUBSEQUENTLY CASTING ADDITIONAL LIQUID POLYMERIZABLE MATERIAL IN SAID ANNULAR SPACE AND POLYMERIZING SAID ADDITIONAL MATERIAL WHILE ROTATING SAID CYLINDERS. 